1. Field of the Invention
This invention generally relates to an impact sensor and, more particularly, to an optical impact fuze for initiating a warhead detonation.
2. Prior Art
In many weapon systems utilizing a shaped charge or a nuclear warhead, it is essential that an impact fuze signal provide detonation as quickly as possible after target contact to prevent damage to the warhead and provide a critical standoff distance necessary for optimum performance. Typically, contact detonation requires some form of communication between an impact sensor situated at or near a target contact point on the delivery vehicle and a detonator which, in many cases, resides at the rear of the warhead. Ideally, the impact sensor should produce a fuzing signal within two microseconds of initial contact, although this time period may vary somewhat depending upon the velocity of the warhead and the vehicle.
The prior art contains numerous examples of contact sensors designed to achieve a fuzing signal shortly after impact. Often, an ogive is located at the front of the vehicle and includes a shaped charge which is activaged on impact to provide a stream of particles projected back towards the warhead to initiate warhead detonation. Alternatively, a closure or crusher switch, located at the nose of the vehicle, mechanically or electrically completes a fuzing circuit to provide a fuzing signal on impact. Also known are optical proximity fuzes such as disclosed by U.S. Pat. No. 4,036,142 providing a fuzing signal upon sensing a substantial change in the reflected or ambient light at the fuze. These prior art devices require materials to be placed at the nose of the vehicle and in front of the blase jet in its formative stages.
Some warheads are provided with optical seekers, and these require an optically transparent dome in order to provide an unobstructed view. Impact sensors of the prior art can, therefore, not be placed on the dome of the vehicle. As a result, impact sensors are placed aft of the dome and detect a stress wave generated by impact in order to provide a detonation signal. Because the stress wave must travel from the point of impact to the sensor, a delay results of approximately 2.5 microseconds per centimeter of distance travelled. In addition, the wave is spread and attenuated resulting in an increased delay between target contact and detonation which can significantly increase the delay between initial contact and fuzing.